One important criteria for safely operating a motor vehicle is the maintenance of proper pressure within tires of the vehicle. If tire pressure is not maintained, fuel economy is adversely affected and rates of tire wear increase. Additionally, handling of the vehicle can be adversely affected and the potential for abrupt failure of the tire is increased. Hence, it is advisable to monitor the pressure within vehicle tires on a regular basis.
One of the difficulties encountered in such regular tire pressure monitoring is that a significant amount of time is associated with monitoring tire pressure. In particular, a safety cap must be removed from the valve stem (and not misplaced). The gauge must be placed upon the valve stem of the tire. Care must be taken to make sure that a significant amount of air is not lost from the tire during this gauge installation process. The pressure can then be read from the gauge. If the tire pressure is adequate, the procedure is completed for that tire and the next tire can be checked. On a vehicle with multiple tires, this basic routine can be significantly time consuming, decreasing the likelihood that tire pressure monitoring will occur on a sufficiently frequent basis.
Compounding this difficulty is the inconvenience encountered when tire pressure is low and air needs to be added to the tire. First the gauge is removed. Then the vehicle is brought into proximity with a source of compressed air. Then compressed air is added to the tire. Unless an accurate gauge is associated with the source of compressed air, the source of compressed air must be removed after a relatively short period of time and the pressure gauge reinserted on the valve stem to take another reading. Typically, a half a dozen or so filling steps and measuring steps are involved before the tire pressure has been brought to the proper level.
It is known in the prior art to provide tire pressure gauges which are mountable upon a valve stem and which are sufficiently small and lightweight that they can remain mounted to the tire during operation of the tire. While this solves a portion of the problem, the difficulty associated with adding air to the tire is not alleviated. In at least two prior art patents, tire pressure gauges are taught which further allow for a source of compressed air to pass into the valve stem of the tire while the gauge remains upon the valve stem. In particular, U.S. Pat. No. 5,377,539 to LaSalle and U.S. Pat. No. 4,924,697 to Hunt (each incorporated herein by reference in their entirety) disclose tire pressure gauges which can mount on a valve stem of a tire and which also include a port through which compressed air can be added without removing the tire pressure gauge.
The tire pressure gauges taught by LaSalle and Hunt are not entirely satisfactory. In particular, in the case of LaSalle the fill port passes through a center of a face which is read to determine the pressure of the tire. A Bourdon tube supporting an indicator is wrapped around this fill tube. To accommodate this fill port passing through a center of the Bourdon tube, a customized Bourdon tube is required which significantly complicates the manufacture of the gauge taught by LaSalle. Also, reading the pressure indicated by the Bourdon tube is made more difficult by the presence of a valve core in a middle of a face of the gauge.
Another problem associated with most prior art tire pressure gauges is that they require viewing by a user when the vehicle is stopped. Often a low pressure condition (or an excessively high pressure condition) occurs while the vehicle is in motion. By the time the driver feels that the vehicle is not operating properly due to inappropriate tire pressure, often damage has already been done to the tire or wheel, or the driver has already consumed excessive fuel or has placed the vehicle in an unsafe condition should emergency handling be necessitated.
Prior art systems are known which include pressure transducers mounted to tire/wheel assemblies and which transmit this pressure signal to a receiver coupled to a display which the vehicle operator can view while the vehicle is in operation to monitor tire pressure status. For instance, U.S. Pat. No. 5,694,111 to Huang and U.S. Pat. No. 4,970,491 to Saint each teach systems which can sense pressure and allow a driver of a vehicle to monitor this pressure remotely. However, such systems are deficient in numerous respects.
In particular, such systems provide a high degree of complexity (thus increasing cost) and are not simple and intuitive for an operator to use. These systems include multiple channels for the multiple wheels of the vehicle and involve transmission of a large amount of information, such as pressure data for multiple wheels. When a reading is provided on the display which indicates that a tire requires air pressure adjustment, an operator must have a high degree of familiarity with the system to be able to find the appropriate tire, especially on large commercial trucks which can often have eighteen or more wheels. Once the wheel having the improper air pressure is found, the user is still faced with a relatively tedious process of utilizing some additional tire pressure gauge and source of compressed air to alternately adjust the air pressure, take a new tire pressure reading, and continue iteratively until the desired tire pressure is achieved.
Accordingly, a need exists for a tire pressure gauge which has a signal transmission capability but which maintains simplicity and can be easily used to determine which wheel has improper air pressure and which readily facilitates air pressure adjustment.